1. Field of the Invention
This invention relates to a power supply circuit utilizing a charge pump (CHP) type step-up circuit and to a portable device equipped with such power supply circuit and a load circuit such as an LCD driver circuit.
2. Description of the Related Art
CHP type step-up circuits have been used in many of conventional power supply circuits to generate a higher voltage than a power supply voltage.
In general, a CHP step-up circuit has multi-stage CHP units configured to step up an inputted power supply voltage to a desired step-up voltage. Japanese Patent Applications Laid Open No. 2001-157438 (referred to as Patent Document 1) and No. 2003-289663 (referred to as Patent Document 2) disclose CHP step-up circuits having multi-stage CHP units for stepping up an inputted power supply voltages to a desired step-up voltage wherein the number of operable stages of the CHP units is changed based on the detected level of output current and/or the step-up voltage. That is, the CHP step-up circuit is adapted to generate a desired step-up voltage in response to a change in the power supply voltage.
Incidentally, in utilizing a CHP step-up circuit as a power supply circuit for driving a load circuit such as an LCD driver circuit, an output voltage generation circuit is often used to convert the step-up voltage to a predetermined output voltage (namely, internal voltage) of the load circuit. However, when a power supply circuit that includes such a CHP step-up circuit and an output voltage generation circuit as stated above is formed in one IC chip along with a load circuit such as an LCD driver circuit, no means is provided for controlling the step-up voltage in response to an internal voltage.
In the case of an LCD, voltage correction for fine adjustment of colors and, above all, voltage correction to compensate for temperature changes of the IC chip are required. However, the methods taught in the above-mentioned Patent Documents 1 and 2 are not satisfactory for these purposes.